1. Field of the Invention
The invention relates to a method for producing ethylene glycol, and more particularly to a method for producing ethylene glycol from a polyhydroxy compound under hydrothermal conditions.
2. Description of the Related Art
Conventional methods for producing ethylene glycol involve oil as raw material. For example, ethylene is epoxidized to yield ethylene oxide which is hydrated to yield ethylene glycol. Oil is a non-renewable resource and these methods include a step of selective oxidization or epoxidation, which increases the technical difficulty of the process. Furthermore, conventional methods have low efficiency and high material consumption, can produce serious pollution, and produce a large quantity of by-products.
Producing ethylene glycol with renewable raw materials can reduce human dependence on fossil materials and is conducive to achieving sustainable development in terms of both the environment and the economy.
Polyhydroxy compounds, such as starch, hemicellulose, glucose, sucrose, fructose, and fructan, are very common in nature and the yields thereof are on the increase with the development of agricultural technologies. Producing ethylene glycol using polyhydroxy compounds not only reduces human dependence on fossil materials but also improves the added value of agricultural products.
Conventional methods for producing ethylene glycol from polyhydroxy compounds include the steps of: (a) gelatinizing, liquefying, and saccharifying starch to yield glucose; (b) hydrotreating the glucose with ruthenium or nickel as catalyst to yield sorbitol; and (c) degrading the sorbitol by hydrogenolysis under high temperature and high pressure conditions to yield a mixture that mainly includes propylene glycol, glycerol, and ethylene glycol. The yields of ethylene glycol are between 10% and 30% and the preparation methods are complex.